
In weather like this, by the time you've got your windshield and windows brushed off (or shoveled out), you're probably exhausted, or freezing, or both. You figure you'll get the roof later. That's why lots of cars were driving around Madison today still sporting these spiffy white hats. They're cute as hell.
They're also dangerous. The problems is that, while the snow on top gets crustier and harder as time goes by, the foundation tends to give way at unpredictable moments as the car warms up. At first the snow pack seems held to the roof by countless icy, sticky fingers. Then suddenly, with no warning, the bottom layer melts from the warmth of the car and the whole thing can go flying. It might fly backwards when accelerating from a stop sign. No problem, except maybe to annoy the people in the car behind you if it all falls on the hood of their car. The real problem happens the other way around -- when you're in traffic and have to hit your brakes. The whole thing can slide down and cover your windshield, with the crusty snow on top holding it together as a single sheet that just sits there and blocks your vision until you can get out and clear the windshield.
I once saw this happen near Park and University, when a driver braked for student jaywalkers and the snow cap came down on the windshield like a shade. They were blind until they could stop the car (in traffic) and get out and push the snow aside. Nobody was hurt, but it was a close call.
It can take forever to brush a foot of snow off the roof. Forget the brush. Just push the snow off with a shovel -- a few passes will do it. You might be glad you did.